Saw sharpening machine

ABSTRACT

This invention relates to improvements in apparatus adapted to effectively mount various types of circular and/or longitudinal saws for optimum sharpening of each saw along the sawtooth edge of any of said saws. It is universally adapted for sharpening any type of sawtooth carried by substantially any type of saw. This saw sharpening device is provided with a pivotally mounted pivot arm supporting a hardened steel block pivotally mounted thereon adapted to be resiliently held against the outer surface of the longitudinal and/or circular saw to prevent chattering of the saw when engaged by the disc grinder. The said arm can be swung upwardly and away from the saw to disengage and release the steel block from direct contact with the outer surface of the saw; the normal pressure of the block against the saw being governed by a resilient coil spring associated with said pivot arm. This invention embodies an antipressure screw attachment whereby the degree of block pressure against the saw can be minutely decreased without effecting the normal action of a coil spring urging the arm toward the saw. This attachment embodies a controlling screw threaded through the pivot arm, and having its free end to bear against a stationary part of the machine. When the screw is turned in a counterclockwise direction, the pivot arm moves downwardly due to the action of the coil spring. When the screw is turned in a clockwise direction, the pivot arm moves outwardly and upwardly, moving the block minutely away from the outer surface of the saw. It is obvious that this novel construction of the pressure controlling screw mounted with the pivot arm provides a novel means to minutely decrease the pressure between the block and the outer surface of said saw as desired.

United States Patent [72] Inventor George E. Gunderman R. #3, Blissfield. Mich. 49228 [21 I Appl. No. 779,959

[22] Filed Nov. 29, 1968 [4S] Patented June22,l971

[54] SAW SHARPENING MACHINE 7 Claims, 12 Drawing Figs.

Primary ExaminerBemard Stickney Attorney-Anthony J, Castorina ABSTRACT: This invention relates to improvements in apparatus adapted to effectively mount various types of circular and/or longitudinal saws for optimum sharpening of each saw along the sawtooth edge of any of said saws. It is universally adapted for sharpening any type of sawtooth carried by substantially any type of saw. This saw sharpening device is provided with a pivotally mounted pivot arm supporting a hardened steel block pivotally mounted thereon adapted to be resiliently held against the outer surface of the longitudinal and/or circular saw to prevent chattering of the saw when engaged by the disc grinder. The said arm can be swung upwardly and away from the saw to disengage and release the steel block from direct contact with the outer surface of the saw; the normal pressure of the block against the saw being governed by a resilient coil spring associated with said pivot arm. This invention embodies an antipressure screw attachment whereby the degree of block pressure against the saw can be minutely decreased without effecting the normal action of a coil Spring urging the arm toward the saw. This attachment embodies a controlling screw threaded through the pivot arm, and having its free end to bear against a stationary part of the machine. When the screw is turned in a counterclockwise direction, the pivot arm moves downwardly due to the action of the coil spring. When the screw is turned in a clockwise direction, the pivot arm moves outwardly and upwardly, moving the block minutely away from the outer surface of the saw. lt is obvious that this novel construction of the pressure controlling screw mounted with the pivot arm provides a novel means to minutely decrease the pressure between the block and the outer surface of said saw as desired.

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PATENTEU JUhZZ [9H a GEORGE E. GUNDERMAN.

PATENTED JUN22 I972 NJ 3 CF 3 GEORGE E. GUNDEPMAN.

SAW SHARIPENENG MACHENE This invention relates to saw sharpening machines of the general type illustrated in prior art U.S. Pats. Nos. 2,835,146; 2,865,233 and 2,921,484; and is an improvement over the machines disclosed in those patents.

The above-mentioned prior patents show three machines for sharpening circular saws where chattering may occur, the one machine specifically shows means for supporting a lon gitudinal type saw with a stabilizing means. if various operations required by the operator are performed at the proper time and proper sequence, the machines will operate as designed but will not prevent chattering as they lack my invention.

It is the general object of the present invention to provide an improved saw sharpening machine which is less susceptible to improper operation, or chattering of the saw blade while being sharpened by the abrasive grinding wheel disc rotatably mounted on the machine.

With the above points in mind, it is an object of the present invention to provide an improved saw sharpening apparatus of foolproof construction adaptable for sharpening saws of virtualiy any type of saw tooth edge, and embodying antichattering means embodied with the machine and/r attached thereto.

Other objects of the invention will appear from the following description of practical embodiments thereof, when taken in conjunction with the drawings which accompany and form part of this specification.

In the Drawings:

F116. 1 is a perspective view of a saw sharpening apparatus embodying this invention for use in connection with the sharpening of saw blades and preventing chattering of the saw while being sharpened.

FIG. 2 is a fragmentary perspective view on an enlarged scale of a portion of the sharpening machine and showing the pressure controlling screw applied thereto to prevent chattering of the circular sawdisc.

FIG. 3 is a detail perspective view of the pivotal arm embodying the pressure control screw, the arm detached from the other parts of the machine shown in FIG. 1.

HO. 4- is a fragmentary end elevation of the pivotal arm attached to a portion of the machine, a section broken away to show the tension spring within the housing in its lower pressure stage, and showing the free end of the antichatterin g control screw in contact with the machine frame.

F M. 5 is a fragmentary front elevation of the spring housing embodied with the pivotal arm, or clamping lever, a section of the housing broken away showing the tension spring in its high pressure stage, and showing the circular head of the pressure control screw.

MG. 6 is a fragmentary perspective view of the free end of the clamping lever detached from the other parts of the machine and showing the inwardly directed saw-engaging blocl; pivotally mounted therewith and in contact with a fragmentary portion of a circular saw disc.

FIG. 7 is a fragmentary end view on an enlarged scale of a portion of the machine frame, showing a socket therein with the free end portion of the pressure controlling screw arranged therein and in contact therewith.

FIG. 8 is a fragmentary perspective view similar to that shown by FIG. 2, but having an attachment embodying a second saw engaging block secured with the clamping bar, and embodying this invention for preventing chattering of the saw blade being sharpened.

FIG. 9 is a fragmentary end view, similar to FIG. 4, but showing the lower end of the tension spring in low stage and full lines.

H6. 10 is a fragmentary rear view, of the parts shown in FIG. 9, showing the lower end of the tension spring in high stage, or extended position; showing crank arm therewith effecting high pressure.

FIG. ll is a fragmentary top plan view of the saw engaging bar shown in FIG, 8, and

H6. 12 is a front elevational view of the parts shown in FIG. ll, showing the block mounted with the lower side of the pivot arm.

The saw sharpening machine embodying this invention is first described below by its mechanical structure according to FlGS. l, 2, 3 and 4. This machine including a standard, or body member 15 extending upwardly from a base l6 and having a saw supporting carriage l7 movable up and down on a guide l8 and having a pivot, or arbor 19 secured thereto on which a saw 20 may be rotatably mounted. The machine also includes a saw-vise 2i, having a fixed arm 22 secured to the frame of the machine; and a pivot arm 23 sometimes called a clamping lever, both of these arms having the usual parts for engaging opposite faces of a saw so as to frictionally oppose turning of the saw blade about the arbor E9; the bar 24 is horizontally and rigidly mounted at one end to the machine, and having its forward free end adapted to bear against the rear side of the saw blade 20 while the hardened steel contact block 25 is pivotally mounted to the free end 26 of pivot arm 23. The said free end 26 extends rearwardly toward the machine, and the saw thereon, an embodies a yoke with two lugs 27 and 28 cast integrally therewith. A pin 29 extends between the two lugs 27 and 28 and enables the steel block 25 to be pivotally mounted thereon, whereby the vertical contact face 30 of the block 25 will bear against the saw 20 in the same plane. The carriage 37 may be raised or lowered by means of a hand lever 32 for moving the carriage from a lowered position in which the saw blade may be readily mounted thereon, to an upper position in which the saw blade is in position to be sharpened.

The saw-sharpening member 33 is shown in the form of an abrasive wheel or disc mounted on a reciprocable head 34, the saw sharpening disc being rotated by means of a motor 35 supported on the head 34. This head has a reciprocatory movement toward and from the saw 20 and is also shiftable about its upright axis to alternately present the abrasive disc in different angular relations to alternate teeth.

The machine also includes suitable means for turning the saw blade 30 step by step about the pivot l5 to present teeth successively into position to be acted upon by the grinding wheel 33, such means as shown by FIG. l, being a pair of dogs or latches 36 and 37 which advance the saw against the friction produced by the members 24 and 25 in contact with the opposite sides of the saw. A majority of the parts thus far specifically described have been commonly used in connection with saw-sharpening machines and of themselves do not constitute a part of this invention.

This invention centers around the pivot arm 23 and associated parts shown specifically by FIG. 3 through 10. The said pivot arm 23 embodies a hollow housing member 40 embodying yoke portions 41 and 42. A pin 43 extends between the yoke portions 41 and 4-2 and through the free end of the fixed arm 22, and enables the housing 4-6 to be pivotally mounted upon the pin 43. The lower end of the housing embodies a crank arm dd therein which is mounted upon shaft 45 extending through the front wall 46, with control nut 47 mounted thereon and outside the housing. The crank arm 64 has a horizontally arranged pin 48 affixed therewith at its free end. A coil tension spring 50 is arranged in a substantially vertical manner within the housing, said spring having a coiled top end 51 encircling the said pin 43, and having a coiled lower end 52 encircling the pin 48. It is obviously that when the crank 44 is turned clockwise by control nut 47 it lengthens the spring 50 effecting greater spring pressure upon pivot arm 23; causing said block 25 to bear more strongly upon the saw. This action is caused by offcenter alignment of the spring. This action is common practice in these machines so will not be described further except this action produces what is known as a two stage high and low bearing pressure upon a saw.

In accordance with my invention, i provide a pressure control screw 66 extending through the front and rear walls 46 and 4d of housing 40, see FIG. 9. As clearly shown by FlGS. 9 and lid the upper end i of spring 50 extends upwardly and around pin 63 leaving plenty of room in the housing for the screw as to extend therethrough. The forward end of antipressure screw so has a knurled control knob 611 secured thereto whereby turning of the knob til will also turn the shaft on, because the forward half portion of the screw is threaded and cooperate with internal threads in the bores in the front and rear walls 46 and 41%, elevated above the central coils of spring 50. The screw as has an unthreaded portion 64 at the rear end section thereof leaving a cone shaped rear free end 62 which bears in socket 63 in the fixed arm 22; see PM]. 7.

As described above it will be seen that the pivot arm 23 can be pulled manually outwardly away from the saw being sharpened. When a small diameter circular saw is being sharpened and less friction is required to hold the saw stationary while being sharpened, the coil spring is shortened by turning the nut 47 as shown by H6. 9. When a larger saw is being sharpened, more friction is needed, so more pressure must be applied upon block 25; therefore the coil spring is lengthened by turning the nut 47, as shown by HG. Ml. With the two stages of spring pressure as described to stop chattering of the saw being sharpened, the degrees of pressure may not be one hundred percent correct for saws of different grade of steel; chattering will be effected due to incorrect pressures applied thereto. The control knob bl can be turned to decrease the pressure of either stage of coil spring pressure, this decrease of pressure will generally free the excess friction upon the saw and eliminate chattering. The two stages generally produce spring pressures too great for the size and must be decreased slightly, should chattering occur.

Obviously the screw 6t) may be turned counterclockwise by knob 6E, preventing contact of the point 62 of screw 60 to touch the rigid arm 22; leaving the coil spring to effect only two stages of pressure. When the screw db is turned in the opposite direction, the screw point 62 will bear in socket 63 of fixed arm 22. The turning of the screw 60 clockwise will therefore, as will be obvious, force the arm 23 outwardly and upwardly decreasing the spring pressure effected by the coil spring 54). This minute adjustment of screw dill will decrease the pressure, and/or friction of block 25 upon saw 2i), preventing chattering without the necessity of altering the construction of such machines by changing size of coil springs etc. used therewith. My invention prevents excess pressure by block 25 upon the face of the saw; it is a means for varying the friction between the block 25 and the saw 29.

in order to accommodate my invention and machine with longitudinal typed saws, and band saws, an extra pressure block is needed to press against the saw at two or more locations. in F168. 8, ll and 312, an attachment means is shown and will now be described below. The plate 76 is arranged in groove 7ll formed on the under side of the pivobarm 23, extending transversely of the arm 23, substantially midway between the housing 40 and the free end 26 of the pivot arm 23. A transverse slot 73 extends through the arm 23 allowing transverse movement of a locking screw 72. A threaded bore 741 is provided to extend vertically through the plate 7b. The screw 72 extends downwardly through the slot 73 and threaded into the bore 70; the head of the screw being larger than the body thereof so it bears on top of arm 23, counterclockwise tuming of the screw 72 will pull the plate 70 into tight engagement with the arm 23, suitable for locking the plate rigidly thereto. The plate is moved in the slot 73 to bring the rear end 76 of the plate 70 into bearing contact with the saw arranged on the machine. Said rear end 76 is formed with a yoke type section embodying lugs 77 and 78. A pin 7% extends between the lugs 77 and 78 and enables the steel block $0, of rectangular shape, to be pivotallymounted Lhereon, where by the vertical steel face portion 32 thereof will bear against the saw blade of sufficient length and arranged at the rear thereof for sharpening. The plate 76 with block ill) will be set to bear against the saw with the same pressure as the pressure of arm 23 and block 25; the pressure being the same and governed by the coil spring pressure. it will be obvious that my invention as described will be operable to control one or more pressure blocks, the single control screw 60 may be turned clockwise to decrease the pressure and/or friction of both blocks 25 and 80 up a single saw and prevent chattering of the saw while being sharpened by an abrasive disc 33. The block dill provides a pressure upon a saw in substantially the same horizontal plane as occupied by block 25.

While l have shown and described my invention for use in connection with a grinding wheel for sharpening teeth, it will be obvious that my control screw 60 may be assembled to machines in which the sharpening of the teeth is effected by filing instead of grinding.

it will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art, within the principle and scope of the present invention, which is to be interpreted in the light of the prior art and the appended claims only, with due consideration for the doctrine of equivalents.

l claim as my invention:

l. A saw sharpening machine comprising a standard, a saw mounting means mounted on said standard, a movable head slidably mounted on said standard, a grinding disc mounted on the said head, a pressure arm pivotally mounted at its one end to said standard and having a friction type pressure block mounted upon its opposite free end, a spring member attached at one end with said standard and having its opposite end attached to said pressure arm, said spring member normally biasing the movable pressure arm and said pressure block in an approximately horizontal plane toward said saw clamping means to effect frictional contact of said block with 2*. saw to be sharpened and when mounted upon said saw mounting means, and a nonyielding antipressure control screw adjustably mounted with said pressure arm and having its free end in contact with said standard for varying the friction between the pressure block and the saw when mounted upon said saw mounting means.

2. The combination with a saw sharpening machine having a standard and with a saw to be sharpened mounted thereon, of a pressure arm pivotally mounted upon said standard a pressure block mounted upon the free end of said pressure arm for engaging the upper part of said saw frictionally, spring means for biasing said pressure arm toward said standard, and positively acting means for moving the pressure arm away from said standard so that the pressure block will engage the said saw to be sharpened with the desired amount of friction.

3. A saw sharpening machine comprising a machine standard, a saw supporting carriage slidably mounted on the said standard in a saw sharpening region, a reciprocable head mounted on said standard above said carriage, a grinding disc and driving motor mounted upon said head, means to move said head vertically away from and toward the said carriage, a pressure arm pivotally mounted at one end with a rigid part of said standard and movable toward and away from said standard, the free end of said pressure arm extending toward said saw sharpening region and having a friction type contact block pivotally mounted thereon and extending toward said standard, said pivot end of said arm having a bore extending substantially horizontally therethrough embodying internal threads, a screw type metallic control shaft having threads at one end for engagement with said internal threads of said bore and arranged therein, whereby rotation thereof effects reciprocable movement thereof, a coiled, contractable spring connected between the pressure arm and means supported by said standard and tensioned to normally bias the movable pressure arm and control shaft toward the fixed standard effecting the free end of the shaft to contact said standard, and means for rotating said control shaft to effect reciprocable movement toward and away from said standard, to adjust the location and pressure of said contact block relative to said saw-supporting carriage adapted to mount a saw to be sharpened in the saw sharpening region.

4. A saw sharpening machine comprising a machine standard, a saw clamping carriage slidably mounted on the standard in a saw sharpening region, a grinding disc and motor slidably mounted on the standard above said carriage, means to move the grinding disc away from and toward the carriage, an arm extension secured to said standard having a free end, a pressure arm having a hollow housing at one end and a friction block pivotally to its free end, the hollow housing of said arm pivotally attached to the free end of said arm extension by a crosspin extending through the upper portion of said housing, a crank arm mounted in the lower portion of said housing having a lower crank pin extending through a wall of the said housing and having 'a turning means attached to the end thereof and having the upper pin thereof free to oscillate therein, a contractable spring extending within said housing with its upper end connected to said crosspin and its lower end connected to the upper pin of said crank, whereby movement of said turning means connected with said crank effects oscillation of said crank and variation of the tension of said spring, a screw type metallic control shaft extending through said housing, one end of said shaft having external threads thereon mating with internal threads in bores provided in the walls of said housing, a control means attached to the said threaded end of said shaft outside said housing, the opposite end of said control shaft being a free and extending toward said machine standard, said coil spring normally biasing the movable pressure arm and said free end of said control shaft toward the fixed standard effecting said free end to contact said standard, turning of said control means on said control shaft effects reciprocable movement thereof and said pressure arm toward and away from said standard, and effecting movement of said pressure block relative to said saw carriage adapted to mount a saw to be sharpened in the saw sharpening region,

5. A saw sharpening machine comprising a machine standard, a saw supporting carriage slidably mounted on the said standard in a saw sharpening region, a reciprocable head mounted on the standard above the carriage, a grinding disc and driving motor associated therewith being mounted upon said head, means to move said head and said grinding disc vertically away from and toward the said carriage in said saw sharpening region, a pressure arm pivotally mounted at one end with said standard and movable about an axis substantially transverse to the direction of advance movement of said saw supporting carriage and having its free end extending toward and into the saw sharpening region, said pivot arm including a contact friction block pivotally mounted upon its free end and extending into the said saw sharpening region, a screw type control member adjustably secured at one end to said pivot arm and having its free end extending toward said machine standard, spring means attached to said arm biasing the said free end of said control member toward and into direct contact with said standard under spring pressure, and means for adjusting the location of the free end of said screw type control relative to said pivot arm for controlling substantially horizontal movement of said pivot arm and said contact block, so that when said control screw is slightly rotated in one direction while in contact with the standard the pivoted arm may move away from said standard and said contact block out of the saw sharpening region whereby spring pressure exerted through said arm to said block is reduced as desired.

6. The saw sharpening machine defined in claim 3, said pressure arm being of tubular formation forming a housing, and said coiled, contractable spring extending within said tubular housing, a crank arm mounted within said housing and rotatably mounted at the base thereof and having the horizontal pin thereof movable freely in the housing, the lower end of said spring connected to said pin of said crank shaft, means connected with said crank to oscillate said pin and effect movement of said lower end of the said spring whereby its tension is varied.

7. The saw sharpening machine recited in claim 6 wherein said pressure arm is provided with a groove of rectangular configuration in its lower surface intermediate the ends thereof and which 15 in transverse alignment with respect to the longitudinal axes of the arm, a bar of rectangular configuration in plan and in cross section being slidably and adjustably secured in said groove by a locking means movable in a slot extending through said arm and in alignment with said groove, said bar having a metallic friction block pivotally attached to the free end thereof extending toward said standard and providing a second block, whereby said single control shaft adjusts the position and location of both said friction contact blocks relative to a saw supporting carriage. 

1. A saw sharpening machine comprising a standard, a saw mounting means mounted on said standard, a movable head slidably mounted on said standard, a grinding disc mounted on the said head, a pressure arm pivotally mounted at its one end to said stanDard and having a friction type pressure block mounted upon its opposite free end, a spring member attached at one end with said standard and having its opposite end attached to said pressure arm, said spring member normally biasing the movable pressure arm and said pressure block in an approximately horizontal plane toward said saw clamping means to effect frictional contact of said block with a saw to be sharpened and when mounted upon said saw mounting means, and a nonyielding antipressure control screw adjustably mounted with said pressure arm and having its free end in contact with said standard for varying the friction between the pressure block and the saw when mounted upon said saw mounting means.
 2. The combination with a saw sharpening machine having a standard and with a saw to be sharpened mounted thereon, of a pressure arm pivotally mounted upon said standard a pressure block mounted upon the free end of said pressure arm for engaging the upper part of said saw frictionally, spring means for biasing said pressure arm toward said standard, and positively acting means for moving the pressure arm away from said standard so that the pressure block will engage the said saw to be sharpened with the desired amount of friction.
 3. A saw sharpening machine comprising a machine standard, a saw supporting carriage slidably mounted on the said standard in a saw sharpening region, a reciprocable head mounted on said standard above said carriage, a grinding disc and driving motor mounted upon said head, means to move said head vertically away from and toward the said carriage, a pressure arm pivotally mounted at one end with a rigid part of said standard and movable toward and away from said standard, the free end of said pressure arm extending toward said saw sharpening region and having a friction type contact block pivotally mounted thereon and extending toward said standard, said pivot end of said arm having a bore extending substantially horizontally therethrough embodying internal threads, a screw type metallic control shaft having threads at one end for engagement with said internal threads of said bore and arranged therein, whereby rotation thereof effects reciprocable movement thereof, a coiled, contractable spring connected between the pressure arm and means supported by said standard and tensioned to normally bias the movable pressure arm and control shaft toward the fixed standard effecting the free end of the shaft to contact said standard, and means for rotating said control shaft to effect reciprocable movement toward and away from said standard, to adjust the location and pressure of said contact block relative to said saw-supporting carriage adapted to mount a saw to be sharpened in the saw sharpening region.
 4. A saw sharpening machine comprising a machine standard, a saw clamping carriage slidably mounted on the standard in a saw sharpening region, a grinding disc and motor slidably mounted on the standard above said carriage, means to move the grinding disc away from and toward the carriage, an arm extension secured to said standard having a free end, a pressure arm having a hollow housing at one end and a friction block pivotally to its free end, the hollow housing of said arm pivotally attached to the free end of said arm extension by a crosspin extending through the upper portion of said housing, a crank arm mounted in the lower portion of said housing having a lower crank pin extending through a wall of the said housing and having a turning means attached to the end thereof and having the upper pin thereof free to oscillate therein, a contractable spring extending within said housing with its upper end connected to said crosspin and its lower end connected to the upper pin of said crank, whereby movement of said turning means connected with said crank effects oscillation of said crank and variation of the tension of said spring, a screw type metallic control shaft extending through said housing, one end of said shaft having external threads thEreon mating with internal threads in bores provided in the walls of said housing, a control means attached to the said threaded end of said shaft outside said housing, the opposite end of said control shaft being a free and extending toward said machine standard, said coil spring normally biasing the movable pressure arm and said free end of said control shaft toward the fixed standard effecting said free end to contact said standard, turning of said control means on said control shaft effects reciprocable movement thereof and said pressure arm toward and away from said standard, and effecting movement of said pressure block relative to said saw carriage adapted to mount a saw to be sharpened in the saw sharpening region.
 5. A saw sharpening machine comprising a machine standard, a saw supporting carriage slidably mounted on the said standard in a saw sharpening region, a reciprocable head mounted on the standard above the carriage, a grinding disc and driving motor associated therewith being mounted upon said head, means to move said head and said grinding disc vertically away from and toward the said carriage in said saw sharpening region, a pressure arm pivotally mounted at one end with said standard and movable about an axis substantially transverse to the direction of advance movement of said saw supporting carriage and having its free end extending toward and into the saw sharpening region, said pivot arm including a contact friction block pivotally mounted upon its free end and extending into the said saw sharpening region, a screw type control member adjustably secured at one end to said pivot arm and having its free end extending toward said machine standard, spring means attached to said arm biasing the said free end of said control member toward and into direct contact with said standard under spring pressure, and means for adjusting the location of the free end of said screw type control relative to said pivot arm for controlling substantially horizontal movement of said pivot arm and said contact block, so that when said control screw is slightly rotated in one direction while in contact with the standard the pivoted arm may move away from said standard and said contact block out of the saw sharpening region whereby spring pressure exerted through said arm to said block is reduced as desired.
 6. The saw sharpening machine defined in claim 3, said pressure arm being of tubular formation forming a housing, and said coiled, contractable spring extending within said tubular housing, a crank arm mounted within said housing and rotatably mounted at the base thereof and having the horizontal pin thereof movable freely in the housing, the lower end of said spring connected to said pin of said crank shaft, means connected with said crank to oscillate said pin and effect movement of said lower end of the said spring whereby its tension is varied.
 7. The saw sharpening machine recited in claim 6 wherein said pressure arm is provided with a groove of rectangular configuration in its lower surface intermediate the ends thereof and which is in transverse alignment with respect to the longitudinal axes of the arm, a bar of rectangular configuration in plan and in cross section being slidably and adjustably secured in said groove by a locking means movable in a slot extending through said arm and in alignment with said groove, said bar having a metallic friction block pivotally attached to the free end thereof extending toward said standard and providing a second block, whereby said single control shaft adjusts the position and location of both said friction contact blocks relative to a saw supporting carriage. 